Protective structures for bond wires

ABSTRACT

Protective structures for bond wires or other intermediate conductive elements of a semiconductor device assembly cover the intermediate conductive elements without covering a substantial portion of a semiconductor device from which the intermediate conductive elements extend. In addition to coating at least portions of one or more intermediate conductive elements, the protective structure may include a fence which is configured to receive a semiconductor device. Such a fence may be formed integrally with the remainder of the protective structure or a separately formed member. The protective structures may be formed from a photopolymer material which has been at least partially cured, for example, by stereolithography processes. Accordingly, the protective structures may include a single layer or a plurality of superimposed, contiguous, mutually adhered layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 10/641,471,filed Aug. 14, 2003, pending, which is a continuation of applicationSer. No. 09/841,923, filed Aug. 16, 2001, now U.S. Pat. No. 6,611,053,issued Aug. 26, 2003, which is a divisional of application Ser. No.09/590,419, filed Jun. 8, 2000, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to stereolithography and, morespecifically, to the use of stereolithography to fabricate structureson, or components of, semiconductor testing apparatus and to theresulting structures.

2. Background of Related Art

In the past decade, a manufacturing technique termed“stereolithography,” also known as “layered manufacturing,” has evolvedto a degree where it is employed in many industries.

Essentially, stereolithography, as conventionally practiced, involvesutilizing a computer to generate a three-dimensional (3-D) mathematicalsimulation or model of an object to be fabricated, such generationusually effected with 3-D computer-aided design (CAD) software. Themodel or simulation is mathematically separated or “sliced” into a largenumber of relatively thin, parallel, usually vertically superimposedlayers, each layer having defined boundaries and other featuresassociated with the model (and thus the actual object to be fabricated)at the level of that layer within the exterior boundaries of the object.A complete assembly or stack of all of the layers defines the entireobject. Surface resolution of the object is, in part, dependent upon thethickness of the layers.

The mathematical simulation or model is then employed to generate anactual object by building the object, layer by superimposed layer. Awide variety of approaches to stereolithography by different companieshas resulted in techniques for fabrication of objects from both metallicand nonmetallic materials. Regardless of the material employed tofabricate an object, stereolithographic techniques usually involvedisposition of a layer of unconsolidated or unfixed materialcorresponding to each layer within the object boundaries. This isfollowed by selective consolidation or fixation of the material to atleast a semisolid state in those areas of a given layer corresponding toportions of the object, the consolidated or fixed material also at thattime being substantially concurrently bonded to a lower layer. Theunconsolidated material employed to build an object may be supplied inparticulate or liquid form and the material itself may be consolidated,fixed or cured, or a separate binder material may be employed to bondmaterial particles to one another and to those of a previously formedlayer. In some instances, thin sheets of material may be superimposed tobuild an object, each sheet being fixed to a next lower sheet andunwanted portions of each sheet removed, a stack of such sheets definingthe completed object. When particulate materials are employed,resolution of object surfaces is highly dependent upon particle size.When a liquid is employed, resolution is highly dependent upon theminimum surface area of the liquid which can be fixed (cured) and theminimum thickness of a layer which can be generated given the viscosityof the liquid and other parameters, such as transparency to radiation orparticle bombardment (see below) used to effect at least a partial cureof the liquid to a structurally stable state. Of course, in either case,resolution and accuracy of object reproduction from the CAD file is alsodependent upon the ability of the apparatus used to fix the material toprecisely track the mathematical instructions indicating solid areas andboundaries for each layer of material. Toward that end, and dependingupon the layer being fixed, various fixation approaches have beenemployed, including particle bombardment (electron beams), disposing abinder or other fixative (such as by ink-jet printing techniques), orirradiation using heat or specific wavelength ranges.

An early application of stereolithography enabled rapid fabrication ofmolds and prototypes of objects from CAD files. Thus, either male orfemale forms on which mold material might be disposed could be rapidlygenerated. Prototypes of objects could be built to verify the accuracyof the CAD file defining the object and to detect any designdeficiencies and possible fabrication problems before a design wascommitted to large-scale production.

In more recent years, stereolithography has been employed to develop andrefine object designs in relatively inexpensive materials, and has alsobeen used to fabricate small quantities of objects where the cost ofconventional fabrication techniques is prohibitive, such as in the caseof plastic objects conventionally formed by injection molding. It isalso known to employ stereolithography in the custom fabrication ofproducts generally built in small quantities or where a product designis rendered only once. Finally, it has been appreciated in someindustries that stereolithography provides a capability to fabricateproducts, such as those including closed interior chambers or convolutedpassageways, which cannot be fabricated satisfactorily usingconventional manufacturing techniques.

However, to the inventor's knowledge, stereolithography has yet to beapplied to mass production of articles in volumes of thousands ormillions, or employed to produce, augment or enhance products includingother pre-existing components in large quantities, where minutecomponent sizes are involved, and where extremely high resolution and ahigh degree of reproducibility of results are required.

In the electronics industry, computer chips are typically manufacturedby configuring a large number of integrated circuits on a wafer andsubdividing the wafer to form singulated devices or dice. Such dice,including so-called “flip-chip” dice, have “solder bumps” or otherconductors, or conductive structures, for electrically connecting eachdie to circuitry external thereto. These conductors are also useful fortemporary connection of a die to a test circuit to determine its fitnessfor the intended use. Tests may be conducted before or after the die hasbeen packaged.

One type of conventional test apparatus that is used to test theelectrical characteristics of semiconductor devices includes a carriersubstrate, a test substrate positioned on the carrier substrate, and afence disposed over the test substrate. The carrier substrate includesterminals and electrical traces that lead from the terminals tocommunicate with test equipment. Terminals of the carrier substrate arewire bonded to contact pads on the test substrate. The contact pads ofthe test substrate communicate with test pads thereof. The test pads arearranged to correspond to a pattern of conductors, such as solder balls,conductive pillars, bond pads, or other conductive structures of asemiconductor device to be tested. The fence forms an aperture over thetest substrate to facilitate alignment of the semiconductor device to betested relative to the substrate. As a die to be tested is aligned witha test substrate, test pads of the test substrate temporarily mate orcontact the conductors of the semiconductor device. Such test apparatuscan be configured to test bare or minimally packaged semiconductor diceor packaged semiconductor devices, such as ball grid array (BGA)packages and chip-scale packages (CSPs).

Conventionally, the bond wires of a test apparatus have been coveredwith a silicone gel or a nonconductive epoxy “glob-top” material. Assuch materials can flow, the use of such materials typically alsorequires that external fences or walls be used to contain such materialsin the desired locations. Internal fences or walls may also be requiredto prevent such glob top, silicone, and other materials from flowingonto the test pads of a test substrate, which can prevent the electricalconnection of tested semiconductor devices to the test substrate.Otherwise, if flowable materials are used to cover wire bonds, thesematerials may have to be removed from the test pads or from theconductors of the tested semiconductor device to ensure adequateelectrical connections between the test substrate and the semiconductordevice assembled therewith.

In other test apparatus, a photoresist material is used to cover thebond wires that connect a test substrate to a carrier substrate. Whenphotoresist materials are used to protect bond wires, the use of a maskand several exposure and developing steps are required.

Accordingly, there is a need for a method of efficiently and effectivelyprotecting the bond wires of semiconductor device test apparatus, aswell as protective structures and test apparatus formed by such amethod.

SUMMARY OF THE INVENTION

The present invention includes a method of fabricating a protectivestructure over the bond wires of a semiconductor device assembly, suchas the bond wires of the semiconductor device test apparatus thatconnect test pads of a test substrate to a carrier substrate and,thereby, to the semiconductor device test apparatus. The presentinvention also includes semiconductor device assemblies so formed.

A test apparatus embodying teachings of the present invention includes asilicon or other known test substrate with test pads on a surfacethereof for receiving complementarily arranged conductors, or conductivestructures, of a semiconductor device and electrical traces leading fromthe test pads to peripheral portions of the test substrate. The testpads may be substantially flush with the surface of the test substrate,recessed relative to the surface, or protrude from the surface,depending upon the types of conductors on the semiconductor devices tobe tested with the test substrate or upon the configurations ofcomponents of the test apparatus that overlie the test substrate.

The test substrate is secured to a carrier substrate and electricalconnections are formed between terminals of the carrier substrate andthe traces and test pads of the test substrate. Preferably, bond wiresare used to establish the electrical connections between the electricaltraces of the test substrate and their corresponding terminals of thecarrier substrate. The terminals of the carrier substrate are configuredto communicate with known semiconductor device testing equipment.

The test apparatus also has protective structures located over the bondwires. The structures formed in accordance with teachings of the presentinvention may be used to physically protect, seal, and isolate the bondwires of a test apparatus so as to prevent physical damage to andshorting of the bond wires.

A so-called “fence,” which has a large opening therethrough, ispositioned over the test substrate. The fence and the openingtherethrough are configured to seat a semiconductor device face downover the test substrate, aligning the conductors on the semiconductordevice with their corresponding test pads of the test substrate. Theopening through the fence may substantially expose a contact surface ofthe test substrate. The opening through the fence may have a pluralityof vertically extending slots spaced about the periphery thereof, whichprovide additional tolerances at the periphery of the opening tofacilitate the insertion of semiconductor devices into, and theirremoval from, the fence.

As another alternative, the fence or the protective structure mayinclude a relatively thin layer that is positionable over the testsubstrate so as to protect the test substrate from damage during therepeated testing of semiconductor devices. Apertures formed through thethin protective layer of the fence over at least test pads of the testsubstrate allow for contact between the test pads and correspondingconductors of a die to be tested and may be used to facilitate alignmentof the semiconductor device relative to the test substrate.

The present invention employs computer-controlled, 3-D computer-assisteddrafting (CAD) initiated, stereolithographic techniques to rapidly formprecision layers of material to specific surfaces of a test substrateand carrier substrate of a test apparatus.

In the stereolithographic processes that are useful in the presentinvention, one or more layers of a photo-curable liquid, referred toherein as a photopolymer, are sequentially placed on or laterallyadjacent to the item to be covered, and the liquid photopolymer of eachlayer is cured to at least a semisolid state by a precisely directedbeam of laser radiation at substantially ambient temperature. Multiplesuperimposed, contiguous, mutually adhered layers, each separatelycured, form one or more precision three-dimensional structures ofdesired dimensions.

For example, a substrate may be covered with a layer of liquid polyimideor other photopolymer which is cured only in particular locations to anat least semisolid state by precisely directed laser radiation at asubstantially ambient temperature. As the regions of the layer that arecured by the laser may be selected, photopolymer located over certainregions of the substrate, such as the contact pads thereof, may be leftuncured. Thus, apertures may be formed through the protective layersubstantially simultaneously with formation of solid regions of astructure. A single layer having a uniform thickness of, for example,about 25 μm (1 mil) may be formed on the surface of the wafer. Singlelayers having thicknesses of up to about 10 mil or more may be formed,the maximum possible thickness of each layer being limited only by themaximum depth into the liquid photopolymer that the laser beam canpenetrate. Multiple superimposed layers, each separately cured, may beformed to create structure layers of even greater thickness whilemaintaining a thickness accuracy not achievable by conventionaltechniques.

In one embodiment of the method, the bond wire protectors and the fenceare fabricated on a substrate using precisely focused electromagneticradiation in the form of an ultraviolet (UV) wavelength laser to fix orcure a liquid material in the form of a photopolymer. However, theinvention is not so limited and other stereolithographically applicablematerials may be employed in the present invention. The apparatus usedin the present invention may also incorporate a machine vision system tolocate substrates and features on the substrates, such as bond wires andtest pads. The method of the present invention encompasses the use ofall stereolithographic apparatus and the application of any and allmaterials thereby, including both metallic and nonmetallic materialsapplied in any state and cured or otherwise fixed to at least asemisolid state to define a three-dimensional layer or layers havingidentifiable boundaries.

The highly precise stereolithographic process provides accuratealignment of the conductors of a semiconductor device to be tested withthe test pads of the test substrate, providing good electricalconnection without bump deformation.

The bond wire protectors and the fence may be fabricated separately byuse of individual CAD programs. In another embodiment, the fence isformed stereolithographically to be integral with the bond wireprotectors.

Alternatively, a fence can be fabricated on the test and carriersubstrates by other known processes or fabricated separately from thetest apparatus by known processes and subsequently assembled with thetest substrate and carrier substrate assembly. As another alternative, astereolithographically formed fence can be formed separately from theremainder of the test apparatus and then assembled therewith.

Other features and advantages of the present invention will becomeapparent to those of skill in the art through consideration of theensuing description, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The figures of the application illustrate exemplary embodiments of theinvention, wherein the drawings are not necessarily to scale, whereinlike indicia are used for like and similar elements, and wherein:

FIG. 1 is a schematic elevation of an exemplary stereolithographyapparatus suitable for use in practicing the method of the presentinvention;

FIG. 1A is an enlarged portion of FIG. 1 showing a structure of theinvention being formed in a stereolithographic method of the invention;

FIG. 2 is a perspective view of an exemplary test substrate useful forforming a test apparatus of the invention for testing a semiconductorflip-chip die;

FIG. 3 is a perspective view of an exemplary test substrate joined to acarrier substrate for forming a semiconductor device test apparatus ofthe invention;

FIG. 4 is a side cross-sectional view of a test substrate joined to acarrier substrate for forming a semiconductor device test apparatus ofthe invention, as taken along line 4-4 of FIG. 3;

FIG. 5 is a perspective view of a test apparatus of the invention asformed by the method of the invention;

FIG. 6 is a side cross-sectional view of a test apparatus of theinvention, as taken along line 6-6 of FIG. 5;

FIG. 7 is a perspective view of one embodiment of a test apparatus ofthe invention as formed by the method of the invention;

FIG. 8 is a side cross-sectional view of one embodiment of a testapparatus of the invention, as taken along line 8-8 of FIG. 7;

FIG. 9 is a perspective view of another embodiment of a test apparatusof the invention;

FIG. 10 is a side cross-sectional view of another embodiment of a testapparatus of the invention, as taken along line 10-10 of FIG. 9;

FIG. 11 is a side cross-sectional view of another embodiment of a testapparatus of the invention;

FIG. 12 is a perspective view of a further embodiment of a testapparatus of the invention;

FIG. 13 is a side cross-sectional view of a further embodiment of a testapparatus of the invention, as taken along line 13-13 of FIG. 12;

FIG. 14 is a perspective view of another embodiment of a test apparatusof the invention;

FIG. 15 is a side cross-sectional view of another embodiment of a testapparatus of the invention, as taken along line 15-15 of FIG. 14;

FIG. 16 is a perspective view of an additional embodiment of a testapparatus of the invention;

FIG. 17 is a side cross-sectional view of an additional embodiment of atest apparatus of the invention, as taken along line 17-17 of FIG. 16;

FIG. 18 is a perspective view of a test apparatus of the invention witha semiconductor device to be tested inserted into the test apparatus;

FIG. 19 is a side cross-sectional view of a test apparatus of theinvention with a semiconductor device therein, as taken along line 19-19of FIG. 18; and

FIG. 20 is a perspective view of another embodiment of a test apparatusof the invention, showing additional features.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically depicts various components and operation of anexemplary stereolithography apparatus 10 to facilitate the reader'sunderstanding of the technology employed in implementation of thepresent invention, although those of ordinary skill in the art willunderstand and appreciate that apparatus of other designs andmanufacture may be employed in practicing the method of the presentinvention. The preferred stereolithography apparatus for implementationof the present invention, as well as operation of such apparatus, aredescribed in great detail in United States patents assigned to 3DSystems, Inc. of Valencia, Calif., such patents including, withoutlimitation, U.S. Pat. Nos. 4,575,330; 4,929,402; 4,996,010; 4,999,143;5,015,424; 5,058,988; 5,059,021; 5,059,359; 5,071,337; 5,076,974;5,096,530; 5,104,592; 5,123,734; 5,130,064; 5,133,987; 5,141,680;5,143,663; 5,164,128; 5,174,931; 5,174,943; 5,182,055; 5,182,056;5,182,715; 5,184,307; 5,192,469; 5,192,559; 5,209,878; 5,234,636;5,236,637; 5,238,639; 5,248,456; 5,256,340; 5,258,146; 5,267,013;5,273,691; 5,321,622; 5,344,298; 5,345,391; 5,358,673; 5,447,822;5,481,470; 5,495,328; 5,501,824; 5,554,336; 5,556,590; 5,569,349;5,569,431; 5,571,471; 5,573,722; 5,609,812; 5,609,813; 5,610,824;5,630,981; 5,637,169; 5,651,934; 5,667,820; 5,672,312; 5,676,904;5,688,464; 5,693,144; 5,695,707; 5,711,911; 5,776,409; 5,779,967;5,814,265; 5,850,239; 5,854,748; 5,855,718; 5,855,836; 5,885,511;5,897,825; 5,902,537; 5,902,538; 5,904,889; 5,943,235; and 5,945,058.The disclosure of each of the foregoing patents is hereby incorporatedherein by reference. Improvements in the conventional stereolithographicapparatus, as described in copending application Ser. No. 09/259,143,filed Feb. 26, 1999, and of even assignment, relate to a so-called“machine vision” system in combination with suitable programming of thecomputer controlling the stereolithographic process. This improvementeliminates the need for accurate positioning or mechanical alignment ofworkpieces to which material is stereolithographically applied.Alignment of the laser beam or other fixing agent may be item specific(e.g., substrate specific) so that, for example, a plurality ofmicromachined silicon test substrates 40 may be attached to a carriersubstrate 50 and alignment and protective structure 60 (see FIG. 1A)independently formed in selected patterns on each test substrate. Usinga machine vision system, accuracy of the process is not dependent on afiduciary mark 62 (FIG. 2) on a test substrate 40 or on a carriersubstrate 50 but on the visual recognition of specific substratecharacteristics, such as the locations of test pads 42, bond wires 56,or other features of test substrate 40 or carrier substrate 50.

With reference to FIGS. 1-19 and as noted above, a 3-D CAD drawing of anobject such as a protective structure 60 to be fabricated in the form ofa data file is placed in the memory of a computer 12 controlling theoperation of apparatus 10 if computer 12 is not a CAD computer in whichthe original structure design is effected. In other words, an object orstructure design may be effected in a first computer in an engineeringor research facility and the data files transferred via wide or localarea network, tape, disc, CD-ROM or otherwise as known in the art tocomputer 12 of apparatus 10 to fabricate a protective structure 60 orother object comprising one or more applied layers 64 (see FIG. 1A).

Each layer 64 is formed or consolidated from a flowable, curablematerial 16, which is also referred to herein as liquid material 16, bya pass of a laser beam 28 thereinto. Test substrate 40 has an activesurface 38 having test pads 42 thereon. The completed test apparatus 30comprises test substrate 40, carrier substrate 50, and protectivestructure 60 formed over bond wires 56 that electrically connect testsubstrate 40 to carrier substrate 50. The invention relates specificallyto the stereolithographic fabrication of protective structure 60 toshield bond wires 56 of a semiconductor test apparatus.

The data for protective structure 60 is preferably formatted in an STLfile, STL being a standardized format employed by a majority ofmanufacturers of stereolithography equipment. Fortunately, the formathas been adopted for use in many solid-modeling CAD programs, sotranslation from another internal geometric database format is oftenunnecessary. In an STL file, the boundary surfaces of protectivestructure 60 are defined as a mesh of interconnected triangles.

Apparatus 10 also includes a reservoir 14 (which may comprise aremovable reservoir interchangeable with others containing differentmaterials) of liquid material 16 to be employed in applying the intendedlayer(s) 64 of solidified material to test substrate 40 and/or carriersubstrate 50. In a currently preferred embodiment, liquid material 16 isa photo-curable polymer (hereinafter “photopolymer”) responsive to lightin the UV wavelength range. Surface level 18 of the liquid material 16is automatically maintained at an extremely precise, constant magnitudeby devices known in the art responsive to output of sensors withinapparatus 10 and preferably under control of computer 12. A supportplatform or elevator 20, precisely vertically movable in fine,repeatable increments in directions 46 responsive to control of computer12, is located for movement downward into and upward out of liquidmaterial 16 in reservoir 14. A UV wavelength range laser plus associatedoptics and galvanometers (collectively identified as laser 22) forcontrolling the scan of laser beam 26 in the X-Y plane across platform20 has associated therewith mirror 24 to reflect beam 26 downwardly asbeam 28 toward surface 32 of platform 20 or, more particularly, towardactive surface 38 of test substrate 40 and toward surface 54 of carriersubstrate 50 positioned on surface 32. Beam 28 is traversed in aselected pattern in the X-Y plane, that is to say, in a plane parallelto surface 32, by initiation of the galvanometers under control ofcomputer 12 to at least partially cure, by impingement thereon, selectedportions of liquid material 16 disposed over active surface 38 to atleast a semisolid state. The use of mirror 24 lengthens the path of thelaser beam 26, effectively doubling same, and provides a more verticalbeam 28 than would be possible if laser 22 itself were mounted directlyabove platform surface 32, thus enhancing resolution.

Data from the STL files resident in computer 12 is manipulated to buildprotective structure 60 or another object on active surface 38, thesurface of another substrate, or on surface 32 of platform 20 one layerat a time. Accordingly, the data mathematically representing protectivestructure 60 is divided into subsets, each subset representing a layeror slice 64 of protective structure 60. This is effected bymathematically sectioning a 3-D CAD model into a plurality of horizontallayers 64, a “stack” of such layers representing protective structure60. Each slice or layer may be from about 0.0001 to about 0.0300 inchesthick. As mentioned previously, a thinner slice promotes higherresolution by enabling better reproduction of fine vertical surfacefeatures of protective structure 60. In some instances, a base supportor supports 34 (FIG. 1A) for the object (e.g., test apparatus 30) uponwhich protective structure 60 is fabricated may also be programmed as aseparate STL file. Such base supports 34 may be fabricated before theoverlying protective structure 60 and even prior to the disposal of anobject, such as test apparatus 30, on surface 32 of platform 20. Basesupports 34 facilitate fabrication of protective structure 60 withreference to a perfectly horizontal plane. Such base supports alsofacilitate removal of the object (e.g., carrier substrate 50 bearing oneor more test substrates 40 and protective structures 60 from surface 32of platform 20). Where a “recoater” blade 85 is employed, as describedbelow, the interposition of base supports 34 precludes inadvertentcontact of recoater blade 85 with surface 32.

Before fabrication of protective structure 60 is initiated withapparatus 10, the primary STL file for protective structure 60, the filefor the object upon which protective structure 60 is fabricated, and thefile for base support(s) 34 are merged. It should be recognized that,while reference has been made to the formation of a single testapparatus 30, protective structures 60 may be concurrently fabricated onmultiple test apparatus 30 positioned on surface 32 of platform 20. Insuch an instance, the STL files for protective structures 60 andsupports 34, if any, are merged. Operational parameters for apparatus 10are then set, for example, to adjust the size (diameter, if circular) oflaser beam 28 used to cure liquid material 16.

In the exemplary method described herein, test substrate 40 or carriersubstrate 50 may be precisely coated with a structural layer 64irrespective of substrate size or number of test substrates 40. Thus,current stereolithographic equipment will accommodate objects up to 12or more inches in X and Y dimensions, and it is expected that equipmentsize will increase as the need to produce larger groups of testsubstrates 40 becomes commonplace. Bond wires 56 and other structuresmay be totally enclosed without introducing any temperature-induced orflow-induced bending stresses.

As shown in FIG. 1A, base supports 34 may be placed on platform 20 priorto the placement of test apparatus 30 onto platform 20. In addition,lateral supports 36 may be similarly fabricated to secure test apparatus30 to platform 20, preventing lateral movement during fabrication ofprotective structure 60 over bond wires 56 of test apparatus 30. Thefabrication of lateral supports 36 can be facilitated by one or moreindividual STL files or an STL file for lateral supports 36 may bemerged with the other STL files for the entire STL process. Alternativemethods and apparatus for securing test apparatus 30 to platform 20 andimmobilizing test apparatus 30 relative to platform 20 may also be usedand are within the scope of the present invention.

Base supports 34 and lateral supports 36 may be formed of an at leastpartially cured material whose attachment to the platform is readilyreleasable. Alternatively, a solvent may be used to dissolve supports34, 36 to release test apparatus 30 from platform 20 and supports 34,36. Such release and solvent materials are known in the art. See, forexample, U.S. Pat. No. 5,447,822 referenced above and previouslyincorporated herein by reference.

While the invention is described in terms of a liquid materialpolymerizable to a semisolid or a solid state, the process may be variedto use a finely divided, powdered material, for example. The term“unconsolidated” will be used herein to denote the unpolymerizedmaterial which becomes “altered” or “consolidated” by the laserradiation to an at least semisolid state.

As shown in FIG. 2, a test substrate 40 includes a layer 41 of siliconupon which conductive test pads 42 are located. Conductive test pads 42are connected by way of electrical traces 44 to contact pads 48, whichare located at or near the periphery of test substrate 40. Test pads 42may be depressed, raised, or level with active surface 38 of testsubstrate 40 to accommodate the particular type of semiconductor devicesto be tested with test apparatus 30.

As depicted in FIGS. 3 and 4, test substrate 40 is secured on a higherlevel carrier substrate 50, which has contact pads 52 on a surface 54thereof. Contact pads 52 are connected by way of bond wires 56 tocorresponding contact pads 48 (FIG. 3) of test substrate 40. The testsubstrate 40-carrier substrate 50 assembly is secured to platform 20 ofstereolithographic apparatus 10 as already described and shown in FIG.1A. In FIG. 4, traces 44 and contact pads 52 are shown to illustratetheir general location. In the remaining cross-sectional views of FIGS.6, 8, 10, 11, 13, 15, 17, and 19, traces 44 and contact pads 52 are notshown for the sake of clarity.

FIGS. 5 and 6 depict test apparatus 30 of FIGS. 3 and 4, upon which aprotective structure 60 has been formed, such as by thestereolithographic process disclosed herein.

The position and orientation of each test apparatus 30 on whichprotective structure 60 is to be formed is located by scanning platform20 and comparing the features of that test apparatus 30 withcorresponding features stored in the data file residing in memory, thelocational and orientational data for each test apparatus 30 then alsobeing stored in memory. It should be noted that the data filerepresenting the design size, shape and topography for one or more testapparatus 30 on platform 20 may be used at this juncture to detect thosetest apparatus 30 which may be physically defective or damaged. Itshould also be noted that data files for more than one type (size,thickness, configuration, surface topography) of test apparatus 30 maybe placed in computer memory and computer 12 programmed to recognize thelocations and orientations of test substrates 40 and carrier substrates50, as well as of test pads 42, contact pads 48, bond wires 56, contactpads 52, and boundaries 58 which define the protective structure 60which is to be formed, and a laser path for forming protective structure60.

Data from the STL files resident in computer 12 is manipulated to formone layer 64 at a time on test apparatus 30 disposed on platform 20.Accordingly, where the final protective structure 60 is formed of aplurality of individually formed layers 64, the data mathematicallyrepresenting protective structure 60 is divided into subsets, eachsubset representing a slice or layer 64. This is effected bymathematically sectioning the 3-D CAD model into a plurality ofhorizontal layers 64, “stacks” of such layers representing protectivestructures 60. Slices or layers 64 may each be from about 0.0001 toabout 0.0300 inch thick. As mentioned previously, a thinner slicepromotes higher resolution by enabling better reproduction of finevertical surface features of protective structure 60.

Before initiation of a first layer 64 for a support 34, 36 or forprotective structure 60 is commenced, computer 12 automatically checksand, if necessary, adjusts by means known in the art, surface level 18of liquid material 16 in reservoir 14 to maintain same at an appropriatefocal length for laser beam 28. U.S. Pat. No. 5,174,931, referencedabove and previously incorporated herein by reference, discloses onesuitable level control system. Alternatively, the height of mirror 24may be adjusted responsive to a detected surface level 18 to cause thefocal point of laser beam 28 to be located precisely at the surface ofliquid material 16 at surface level 18 if surface level 18 is permittedto vary, although this approach is somewhat more complex. Platform 20may then be submerged in liquid material 16 in reservoir 14 to a depthequal to the thickness of one layer or slice 64 to be formed on testapparatus 30. Surface level 18 of liquid material 16 can be readjustedas required, such as to accommodate liquid material 16-displaced bysubmergence of platform 20. Laser 22 is then activated so that laserbeam 28 will scan liquid material 16 in a defined path over surface 54of carrier substrate 50 or active surface 38 of each test substrate 40of each test apparatus 30, in turn, to at least partially cure (e.g., atleast partially polymerize) liquid material 16 at selected locations oneach test apparatus 30, including around and over bond wires 56.

Boundaries 58 of protective structure 60 circumscribe test substrate 40below active surface 38 and circumscribe a central opening 66 aboveactive surface 38 (see FIG. 5). Central opening 66 has precise innerwall surfaces 86 configured to accurately guide packaged semiconductordevices 80 (or alternatively unpackaged semiconductor devices) (seeFIGS. 18 and 19) thereinto so that the contact pads 82 of semiconductordevice 80 precisely contact test pads 42 for testing each of thesemiconductor devices without the necessity for undue pressure. Theplacement of the inner wall surface 86 is based on the location of testpads 42 (in computer memory) rather than carrier substrate 50, so thataccurate positioning is achieved even when test substrate 40 is joinedto carrier substrate 50 in a less accurate fashion. The outer boundaries58A of protective structure 60 are shown as being in agreement with theedges 88 of carrier substrate 50, but need not be.

If a recoater blade 85 is employed, the process sequence is somewhatdifferent. In this instance, surface 32 of platform 20 is lowered intoliquid material 16 below surface level 18, then raised thereabove untilit is precisely a thickness 96 (see FIG. 1A) of layer 64 below recoaterblade 85. Recoater blade 85 then sweeps horizontally over the uppermostsurface of protective structure 60 on which the next layer is to beformed to remove excess liquid material 16 and leave a film thereof ofthe precise, desired thickness on the uppermost surface. Platform 20 isthen lowered so that the surface of the film and surface level 18 arecoplanar and the surface of liquid material 16 is still. Laser 22 isthen initiated to scan with laser beam 28 and define the first layer 64on surface 54 of carrier substrate 50. The process is repeated, layer bylayer, to define each succeeding layer 64 and simultaneously bond sameto the next lower layer 64 until protective structure 60 is completed. Amore detailed discussion of this sequence and apparatus for performingsame is disclosed in U.S. Pat. No. 5,174,931, previously incorporatedherein by reference. In general, recoater blade 85 cannot be used whereany portion of test substrate 40, carrier substrate 50, bond wires 56,or another feature of test apparatus 30 protrudes upwardly above thesweeping portion of recoater blade 85. Recoater blade 85 may generallybe used for forming only an upper portion of protective structure 60.

As an alternative to the above approach to preparing a layer of liquidmaterial 16 for scanning with laser beam 28, a layer of liquid material16 may be formed on test apparatus 30 by lowering platform 20 to floodmaterial over surface 54 or over the highest completed layer 64 ofprotective structure 60, then raising platform 20 and horizontallytraversing a so-called “meniscus” blade across platform 20 (or justacross the formed portion of protective structure 60) to form a layer 64of desired thickness thereabove, followed by initiation of laser 22 andscanning of beam 28 to define the next higher layer of protectivestructure 60.

As yet another alternative to layer preparation of liquid material 16,platform 20 can be lowered to a depth equal to that of a layer 64 ofliquid material 16 to be scanned and a combination flood bar andmeniscus bar assembly can be horizontally traversed over platform 20 tosubstantially concurrently flood liquid material 16 over surface 54 anddefine a layer 64 of precisely a desired thickness of liquid material 16for scanning.

All of the foregoing approaches to flooding and layer definition andapparatus of initiation thereof are known in the art, so no furtherdetails relating thereto will be provided.

Each layer of protective structure 60 is preferably built by firstdefining any internal and external object boundaries 58, 58A of thatlayer with laser beam 28, then hatching solid areas of protectivestructure 60 with laser beam 28. If a particular part of a particularlayer 64 is to form a boundary 58 of a void in the object above or belowthat layer, then laser beam 28 is scanned in a series of closely spaced,parallel vectors so as to develop a continuous surface, or skin, withimproved strength and resolution. For example, laser 22 first definesboundaries 58 of protective structure 60 in first layer 64 and fills insolid portions of layer 64 within boundaries 58 to complete a layer ofprotective structure 60. Platform 20 is then lowered by a distancesubstantially equal to a desired thickness of the next, second layer 64,and laser beam 28 scanned over the next, second layer 64 to defineboundaries of protective structure 60 therein and to fill in the areasof second layer 64 within boundaries 58 while simultaneously bonding thesecond layer to the first. Additional layers 64 are then added at leastpartially atop the previously formed layer as needed to completeprotective structure 60. The time it takes to form each layer 64 dependsupon its geometry, surface tension and viscosity of liquid material 16,and thickness of the layer.

Once protective structure 60 is completed on test apparatus 30 oranother substrate, platform 20 is elevated above surface level 18 ofliquid material 16, and test apparatus 30 may be removed from apparatus10. Excess, uncured liquid material 16 on the surface of test apparatus30 may be removed, for example, by a manual removal step and solventcleaning. Protective structure 60 on each test apparatus 30 may thenrequire postcuring, as liquid material 16 may be only partiallypolymerized and exhibit only a portion (typically 40% to 60%) of itsfully cured strength. Partially consolidated material or unconsolidatedmaterial in contact with at least partially consolidated material willeventually cure due to the cross-linking initiated in the outwardlyadjacent photopolymer. Postcuring to completely harden protectivestructure 60 or portions thereof may be accelerated in another apparatusprojecting UV radiation in a continuous manner over protective structure60 and/or by thermal completion of the initial, UV-initiated partialcure.

In the embodiment of FIGS. 5 and 6, protective structure 60 is shown asformed to encapsulate and protect bond wires 56 and to provide a topsurface 68 to which a preformed fence member 90 may be bonded. In FIGS.7 and 8, a preformed fence member 90 is shown bonded to top surface 68with a thin layer 92 of adhesive. Fence member 90 has a central opening67 that is generally co-aligned with central opening 66 of protectivestructure 60, although central opening 66 may be larger than centralopening 67. Fence member 90 is positioned to provide accurate mating ofcontact pads on a type of semiconductor device to be tested withcorresponding test pads 42.

Fence member 90 may, by way of example and not limitation, be formed ofplastic, ceramic, semiconductor material such as silicon, or glass(e.g., borophosphosilicate glass (BPSG), borosilicate glass (BSG), orphosphosilicate glass (PSG)). Alternatively, the stereolithographyprocesses disclosed herein may be used to form a fence member 90 of thedesired configuration. When stereolithography is used, fence member 90can be fabricated separately from test apparatus 30 or protectivestructure 60, directly on protective structure 60, or integrally withprotective structure 60.

The external terminals used with test apparatus 30 may be of any typewhich enables reliable electrical connection with test circuitry. Thus,a wide variety of external terminals may be used, including wire-contactpads, solder bumps, tabs, pins, and the like, and are not shown in thedrawings with the exception of FIGS. 7 and 8. In FIGS. 7 and 8, externalterminals are illustrated as exemplary down-formed tab conductors 94.

In practicing the present invention, a commercially availablestereolithography apparatus operating generally in the manner as thatdescribed with respect to apparatus 10 of FIG. 1 is preferably employed.For example and not by way of limitation, the SLA-250/50HR, SLA-5000 andSLA-7000 stereolithography systems, each offered by 3D Systems, Inc., ofValencia, Calif., are suitable for practice of the present invention.Photopolymers believed to be suitable for use in practicing the presentinvention include Cibatool SL 5170 and SL 5210 resins for theSLA-250/50HR system, Cibatool SL 5530 resin for the SLA-5000 system andCibatool SL 7510 resin for the SLA-7000 system. All of these resins areavailable from Ciba Specialty Chemicals Inc. Materials are selected fordielectric constant, sufficient purity (semiconductor grade), adherenceto other semiconductor device materials, desirable hardness for physicalprotection, low shrinkage upon cure, and a coefficient of thermalexpansion (CTE) sufficiently similar to that of test substrate 40 andcarrier substrate 50 of test apparatus 30, to which the material isapplied. By selecting a photopolymer with a CTE similar to those ofsubstrates 40 and 50, substrates 40 and 50 and the at least partiallycured material thereon will not be unduly stressed during thermalcycling in initial testing at elevated temperature and subsequent normaloperation as a semiconductor device test apparatus 30. One area ofparticular concern in determining resin suitability is the substantialabsence of mobile ions and, specifically, fluorides. Layer thickness 96of liquid material 16 to be formed, for purposes of the invention, mayvary widely depending upon the required apparatus height for holdingsemiconductor device 80 to be tested, but will enclose bond wires 56 andmay be configured to apply a dielectric coating over electrical traces44 on active surface 38 of test substrate 40 or other protective coatingon active surface 38.

The size of the laser beam “spot” 78 impinging on the surface of liquidmaterial 16 to cure same may be on the order of 0.002 inch to 0.008inch. Resolution is preferably ±0.0003 inch in the X-Y plane (parallelto platform surface 31) over at least a 0.5 inch×0.25 inch field from acenter point, permitting a high resolution scan effectively across a 1.0inch×0.5 inch area. Of course, it is desirable to have substantiallythis high a resolution across the entirety of surface 54 of a largestructure to be scanned by laser beam 28, such area being termed the“field of exposure.” The longer and more effectively vertical the pathof laser beam 26/28, the greater the achievable resolution.

Referring again to FIG. 1 of the drawings, improved performance of thisprocess is achieved by certain additions to apparatus 10. As depicted,apparatus 10 includes a camera 70 which is in communication withcomputer 12 and preferably located, as shown, in close proximity tomirror 24 located above test apparatus 30. Camera 70 may be any one of anumber of commercially available cameras, such as capacitative-coupleddischarge (CCD) cameras available from a number of vendors. Suitablecircuitry as required for adapting the output of camera 70 for use bycomputer 12 may be incorporated in a board 72 installed in computer 12,which is programmed, as known in the art, to respond to images generatedby camera 70 and processed by board 72. Camera 70 and board 72 maytogether comprise a so-called “machine vision system,” and specificallya “pattern recognition system” (PRS), the operation of which will bedescribed briefly below for a better understanding of the presentinvention. Alternatively, a self-contained machine vision systemavailable from a commercial vendor of such equipment may be employed.For example, and without limitation, such systems are available fromCognex Corporation of Natick, Mass. The apparatus of the exemplaryCognex BGA Inspection Package™ or SMD Placement Guidance Package™ may beadapted to the present invention, although it is believed that theMVS-8000™ product family and the Checkpoint® product line, the latteremployed in combination with Cognex PatMax™ software, may be especiallysuitable for use in the present invention.

It is noted that a variety of machine vision systems are in existence,examples of which and their various structures and uses are described,without limitation, in U.S. Pat. Nos. 4,526,646; 4,543,659; 4,736,437;4,899,921; 5,059,559; 5,113,565; 5,145,099; 5,238,174; 5,463,227;5,288,698; 5,471,310; 5,506,684; 5,516,023; 5,516,026; and 5,644,245.The disclosure of each of the immediately foregoing patents is herebyincorporated herein by this reference.

In order to facilitate practice of the method of the present inventionwith improved apparatus 10, a data file representative of the substratesurfaces 54 on which a protective structure 60 is to be formed is placedin the memory of computer 12. The data file will contain information,such as surface dimensions (in three dimensions) and visual features, aswell as spacing and layout of features (e.g., test pads 42, contact pads48, bond wires 56, and contact pads 52) on test substrate 40 and carriersubstrate 50. The data file will also contain information definingboundaries 58, 58A of protective structure 60 to be formed and, inaddition, a defined path of laser beam 28 as controlled by mirror 24 toachieve the coverage.

Continuing with reference to FIGS. 1 and 1A of the drawings, a testapparatus 30 on platform 20 may be submerged partially below surfacelevel 18 of liquid material 16 to a depth the same as, or greater than,the desired thickness 96 of a first layer 64 of liquid material 16 to beat least partially cured to a semisolid state. Then platform 20 israised to a depth equal to the layer thickness 96 (if previously loweredto a greater depth than a layer thickness) and surface level 18 ofliquid material 16 is allowed to stabilize. Liquid material 16 selectedfor use in applying layer 64 to test apparatus 30 may be one of theabove-referenced resins from Ciba Specialty Chemicals Inc. Inasmuch asthe stereolithography process is conducted without appreciabletemperature rise, the need to compensate boundary location (asconstructed) for subsequent temperature drop to match semiconductordevice dimensions is generally insignificant.

Camera 70 is initiated to locate the position and orientation of eachtest apparatus 30 on which one or more protective structures 60 are tobe formed by scanning platform 20 and comparing the features of testapparatus 30 with those in the data file residing in memory, thelocational and orientational data for each test apparatus 30 then alsobeing stored in memory.

Laser 22 is then activated and scanned to direct beam 28, under controlof computer 12, across the desired portion of carrier substrate 50 toeffect the partial cure of liquid material 16 to form first layer 64.For forming a second and subsequent layers 64, platform 20 is loweredinto reservoir 14 and raised as before, and the laser activated to formthe next layer atop layer 64, for example. It should be noted that layerthickness 96 of liquid material 16 in a selected portion of a givenprotective structure 60 may be altered layer by layer, again responsiveto output of camera 70 or one or more additional cameras 74 and 76 shownin broken lines, which detect particular features of certain testapparatus 30.

It should be noted that the laser treatment may be carried out to form aboundary 58 which adheres to substrate surface 54 or the surface ofprevious layer 64 and the layer within the boundary is lightly cured toform a semisolid “skin” which encloses liquid material 16. The finalcure of protective structure 60 may be effected subsequently bybroad-source UV radiation in a chamber or by thermal cure in an oven. Inthis manner, an extremely precise protective structure 60 may be formedin minimal time within apparatus 10.

As illustrated in FIGS. 9, 10 and 11, fence member 90 may be configuredwith portions 100 having reduced elevation. These portions may have anyshape, including sloped portions 100A (FIGS. 9 and 10) and slottedportions 100B (FIG. 11). Sloped portions 100A and slotted portions 100Bmay be useful for manipulation of a semiconductor device (not shown)inserted into central opening 66 of protective structure 60. Use of suchportions also reduces the quantity of material used to construct fencemember 90.

In another embodiment of the invention, a test apparatus 30 is formedwithout the use of a preformed fence member 90. Thus, as illustrated inFIGS. 12 through 15, the formation of protective structure 60 previouslyshown in FIGS. 5 and 6 is continued to a desirable higher elevation toprovide a guide for semiconductor devices 80 inserted into centralopening 66. In this embodiment, use of a separately formed fence member90 is unnecessary.

In FIGS. 14 and 15, a test apparatus 30 is shown with cut-out wallportions 100 as previously described.

As depicted in FIGS. 16 and 17, protective structure 60 may include athin layer 104 of dielectric material formed over an inner portion ofactive surface 38 of test substrate 40 to protect active surface 38,including electrical traces 44 (not shown) from damage or shorts underrepeated use. Layer 104 may also be useful for protecting asemiconductor device during assembly thereof with test apparatus 30.While layer 104 may be formed by conventional methods, this inventionencompasses the incorporation of its construction as a part of thestereolithography process. Layer 104 can have one or two sublayers ofmaterial that are at least partially cured to give layer 104 a thicknessof about 10 to about 50 μm, but layer 104 may have any thickness thatwill permit the formation of electrical connections between testsubstrate 40 and conductive elements of a semiconductor device to beassembled therewith. As shown, test pads 42 are left uncovered,eliminating any additional step to remove cured material therefrom. Themethodology is incorporated as a STL file into the totalstereolithography program.

FIGS. 18 and 19 show a completed test apparatus (exterior terminals notshown) of the type illustrated in FIG. 12, with a semiconductor device80 inserted therein for testing. In addition, the gap 106 betweencentral opening 66 and semiconductor device 80 is precisely configuredto facilitate insertion of semiconductor device 80 into central opening66 and to align contact pads 82 of semiconductor device 80 or otherconductors communicating therewith and the corresponding test pads 42.In the various embodiments of this invention, a minimum of downwardforce 108 is required to maintain electrical contact between all contactpads 82 of semiconductor device 80 and the corresponding test pads 42 oftest substrate 40. If conductors, such as the illustrated solder balls84, protrude from contact pads 82 of semiconductor device 80, solderballs 84 or other conductors need not be deformed to provide asufficient electrical connection.

It should be noted that in any of the embodiments described thus far,the inner wall surfaces 86 of central opening 66 may be vertical, slopedslightly inward, sloped slightly outward, or undercut (see, e.g., FIG.7). In addition, as shown in FIG. 20, inner wall surfaces 86 may havevertically extending slots 98, or notches. Such slots 98 reduce thefrictional forces in inserting or removing a semiconductor device 80 tobe tested and also result in material savings, weight reduction, andreduced manufacturing time.

Also shown in FIG. 20 are various optional open spaces 102 in protectivestructure 60, which result in weight, material and time savings. Openspaces 102 may be located anywhere in protective structure 60, so longas their location does not hinder the testing of semiconductor devices80 or reduce the useful life of test apparatus 30. Each of thesefeatures is incorporated into the STL data file.

It is notable that the present invention provides a rapid method forforming structures of protective material precisely on specified areasof test apparatus 30. The method is frugal of liquid material 16, sinceall such material in which cure is not initiated by laser beam 28remains in a liquid state in reservoir 14 for continued use.

The method of the present invention is conducted at substantiallyambient temperature, the small laser beam spot 78 size and rapidtraverse of laser beam 28 on test substrate 40, carrier substrate 50,bond wires 56, and other features of test apparatus 30 resulting innegligible thermal stress thereon.

Furthermore, forming a protective structure 60 on a test apparatus 30 bystereolithographic processes is advantageous in that such processesenhance the precision of material placement and the precision with whichstructures of desired dimensions can be fabricated, reduces fabricationtime, reduces subsequent packaging costs, and enables computer controlof the protective structure fabrication process using commerciallyavailable equipment.

Referring to FIGS. 1 through 20 of the drawings, it will be apparent tothe reader that the present invention involves a substantial departurefrom prior applications of stereolithography, in that the structures ofpreformed electrical components are modified by forming multilayeredstructures thereon using computer-controlled stereolithography.Moreover, the use of stereolithography facilitates the fabrication ofprotective structures 60 that have different configurations and are madefrom different materials than existing bond wire protective structures.

It should be re-emphasized that the stereolithographic technique of thepresent invention is suitable for covering, or leaving uncovered, anydesired portion of a substrate, so that electrical connections forconnection to semiconductor devices and other devices may be left bare,eliminating a material removal step.

While the present invention has been disclosed in terms of certainpreferred embodiments, those of ordinary skill in the art will recognizeand appreciate that the invention is not so limited. Additions,deletions and modifications to the disclosed embodiments may be effectedwithout departing from the scope of the invention as claimed herein.Similarly, features from one embodiment may be combined with those ofanother while remaining within the scope of the invention.

1. A protective sheath for at least one elongate conductive element, comprising dielectric material and surrounding at least a portion of the at least one elongate conductive element without covering a substantial portion of a semiconductor device component from which the at least one elongate conductive element extends.
 2. The protective sheath of claim 1, wherein a nonperipheral portion of the semiconductor device component remains exposed beyond or through the dielectric material.
 3. The protective sheath of claim 2, wherein the semiconductor device component comprises an interposer, a carrier, or a test substrate.
 4. The protective sheath of claim 3, further comprising a fence member configured to receive a semiconductor device.
 5. The protective sheath of claim 4, wherein the fence member comprises a plurality of adjacent, mutually adhered regions.
 6. The protective sheath of claim 5, wherein the plurality of adjacent, mutually adhered regions comprises a plurality of superimposed, contiguous, mutually adhered layers.
 7. The protective sheath of claim 1, comprising a plurality of adjacent, mutually adhered regions.
 8. The protective sheath of claim 7, wherein the plurality of adjacent, mutually adhered regions comprises a plurality of superimposed, contiguous, mutually adhered layers.
 9. The protective sheath of claim 1, wherein the semiconductor device component comprises a semiconductor device.
 10. The protective sheath of claim 1, wherein the dielectric material comprises a photopolymer.
 11. The protective sheath of claim 1, substantially surrounding at least a portion of the at least one elongate conductive element.
 12. A protective sheath for at least one elongate conductive element, comprising dielectric material surrounding an entire periphery of at least a portion of the one elongate conductive element.
 13. The protective sheath of claim 12, wherein the dielectric material comprises at least partially cured photopolymer.
 14. The protective sheath of claim 12, comprising at least a portion of a fence member configured to receive a semiconductor device
 15. The protective sheath of claim 14, wherein the fence member comprises a plurality of adjacent, mutually adhered regions.
 16. The protective sheath of claim 15, wherein the plurality of adjacent, mutually adhered regions comprise a plurality of superimposed, contiguous, mutually adhered layers. 